MySQL连接抛出；提供给mysql的未知准备语句处理程序（0）“U stmt”precheck”；错误

我创建了一个macOS应用程序来学习和测试本地MySQL连接

我通过自制安装了MySQL

我可以从应用程序连接到本地主机

我试图使用不存在的数据库名MySQL连接服务器，MySQL抛出未知数据库“测试”

使用现有数据库名称时，会出现以下错误：

Unknown prepared statement handler (0) given to mysql_stmt_precheck

我的连接代码：

import PerfectHTTP
import PerfectHTTPServer
import PerfectMySQL
import Foundation

public class DB {

    let host = "127.0.0.1"
    let user = "root"
    let password = "12345678"
    let database = "pets"
   
    func databaseConnect(host: String, user: String, password: String, db: String) -> MySQL {
        
        let mysql = MySQL() // Create an instance of MySQL to work with
        
        let connected = mysql.connect(host: host, user: user, password: password, db: db)
        
        guard connected else {
            // verify that we have connected successfully
            print(mysql.errorMessage())
            return mysql
        }
        
        return mysql
    }
    
    public func insertGame(title: String, description: String, createdDate: String){
    
        // Connect to our database
        var db = databaseConnect(host: host, user: user, password: password, db: database)
        
        defer {
            db.close() //This defer block makes sure we terminate the connection once finished, regardless of the result
        }
        
        // Create the statement we wish to execute
        let statement = MySQLStmt(db)
        let insert = "INSERT INTO game(id, title, description, release_date) VALUES (\(statement.insertId()), '\(title)', '\(description)', '\(createdDate)');"
        _ = statement.prepare(statement: insert)
        
        // Run the query
        let querySuccess = statement.execute()
        
        // Check that our query was successfuly, otherwise return out
        guard querySuccess else {
            print(db.errorMessage())
            return
        }
        
        print("Insert successful!");
    }
    
}

---

您不应该在

INSERT

语句本身中使用

insertId

（它只是在调用）。该函数获取以前执行的

INSERT

语句的id，由于没有以前的语句，它将失败

您只需从

INSERT

语句中省略

AUTO_INCREMENT

列，让MySQL自己设置自动递增值。这显然假设您将其定义为一个自动递增列，例如

现在，如果在

INSERT

之后，如果您需要自动递增键使用的值，那么您可以调用

insertId

。例如：

func databaseConnect(host: String, user: String, password: String, db: String) -> MySQL? {
    let mysql = MySQL() // Create an instance of MySQL to work with

    let connected = mysql.connect(host: host, user: user, password: password, db: db)

    // verify that we have connected successfully
    guard connected else {
        print(mysql.errorCode(), mysql.errorMessage())
        return nil
    }

    return mysql
}

@discardableResult
public func insertGame(title: String, description: String, createdDate: String) -> UInt? {
    // Connect to our database
    guard let db = databaseConnect(host: host, user: user, password: password, db: database) else {
        return nil
    }

    // Create the statement we wish to execute
    let statement = MySQLStmt(db)
    let insert = "INSERT INTO game (title, description, release_date) VALUES (?, ?, ?);"
    guard statement.prepare(statement: insert) else {
        print(db.errorMessage())
        return nil
    }

    // bind values to the ? in the prepared SQL
    statement.bindParam(title)
    statement.bindParam(description)
    statement.bindParam(createdDate)

    // Check that our query was successfuly, otherwise return out
    guard statement.execute() else {
        print(db.errorMessage())
        return nil
    }

    // if you really need the ID, this is where you'd call `insertId`, perhaps returning it in case the caller would need it
    let id = statement.insertId()
    return id
}

---

上述代码片段中还包含一些其他不相关的问题：

• 我建议不要使用字符串插值来构建SQL。如果标题是“Finnegan's Wake”，名称中的撇号将搞乱SQL，过早终止该字符串值，该怎么办。理想情况下，您可以像上面那样将值绑定到占位符，或者至少使用一些转义逻辑。问题中的SQL容易受到SQL注入攻击和/或需要转义字符串的语法错误的影响

• 我不会建议使用

  \=语句。准备（…）

  模式。返回值的全部意义在于告诉您它是否成功。如果

  prepare

  失败，您将检查错误消息并退出该功能

• 我建议只有在与服务器连接成功时才能继续。在您的报告中，您报告了第二条“MySQL服务器已离开”消息。这仅仅是因为当连接失败时，您正试图与MySQL进行交互，并且您正在继续